Can vacuum fluctuations change the position of an electron? According to QFT, virtual electron-positron pairs are created everywhere in the space, and more frequently near electric charges. Suppose that one such a pair is created in the proximity of an electron. Is it possible for the initial electron to annihilate with the created positron, leaving behind the created electron?
If so, the position of the created electron would not be the same as the initial electron, so this effect would change the position of the electron we observe in that region of the space, creating some kind of uncertainty in position. Is there any quantitative measure of such an uncertainty in position due to vacuum fluctuations?
 A: 
According to QFT, virtual electron-positron pairs are created everywhere in the space, 

Vacuum loops in space have no meaning if there is no incoming or outgoing energy , an interaction, because they have zero energy by themselves, i.e. they are virtual, a mathematical construct.

and more frequently near electric charges

This "more frequently" should be "always"  for the electromagnetic loops, see my answer here about  vacuum fluctuations.
In calculations with Feynman diagrams higher order terms come with such loops of particle antiparticle which correct the energy levels, look at the Lamb shift..
In this sense the probability of finding an electron at (x,y,z,t), the orbital, is modified, but it is not a simplistic exchange of positions , it is a quantum mechanical calculable interaction. 

Is there any quantitative measure of such an uncertainty in position due to vacuum fluctuations?

From vacuum fluctuation without interaction, no. From higher order loop corrections yes, as the orbitals change. It is all about quantum field theory and higher order corrections to the interactions.
